Methods of operating power semiconductor devices and structures

ABSTRACT

Power semiconductor devices, and related methods, where majority carrier flow is divided into paralleled flows through two drift regions of opposite conductivity types.

CROSS-REFERENCE

Priority is claimed from U.S. provisional application 61/361,540 filed 6Jul. 2010, and U.S. provisional application 61/494,205 filed 7 Jun.2011, both of which are hereby incorporated by reference.

BACKGROUND

The present application relates to power semiconductor devices, and moreparticularly to vertical and lateral conduction devices which includeimmobile electric charge which statically inverts a semiconductor driftregion.

Note that the points discussed below may reflect the hindsight gainedfrom the disclosed inventions, and are not necessarily admitted to beprior art.

Power MOSFETs are widely used as switching devices in many electronicapplications. In order to minimize the conduction power losses it isdesirable that power MOSFETs have a low specific on-resistance (R_(SP)or R*A), which is defined as the product of the on-resistance of theMOSFET multiplied by the active die area. In general, the on-resistanceof a power MOSFET is dominated by the channel and drift regionresistances.

Recently, inventions have been disclosed that incorporate fixed orpermanent charges Q_(F) in trenches filled with dielectric material suchas silicon oxide (SiO₂). See for example US patent application20080164518 which is hereby incorporated by reference. Positivepermanent electrostatic charge can be formed within a device structureby, for example, implanting ions such as Cesium into a dielectric (suchas SiO2).

FIG. 19 shows an example of such structures. In the MOSFET structureshown in FIG. 19 the gate electrode is formed in the same trench wherethe lower part is filled with a dielectric material that includesimmobile positive electrostatic charge. The positive permanent chargesbalance the P layer's negative depletion charge in the off-state. Thepositive permanent charge also forms an induced electron drift region byforming an inversion layer along the interface between the oxide and theP layer. The induced inversion layer provides a path for electronscurrent flowing from the source and the channel to the drain.

In order to provide current continuity from the channel to the inducedinversion layer, the gate electrode has to be in close proximity to theinduced electron drift region. Therefore, special care is needed infabricating such devices, in order to achieve both proper functionalityand acceptable gate oxide reliability.

SUMMARY

The present application discloses several different inventions which invarious ways, whether together or separately, provide multiple currentpaths, improved current spreading, improved device reliability, and/orimproved processing simplicity. Many embodiments combine a dynamicallyinverted channel region with a statically inverted drift region, inseparate locations of first-conductivity-type semiconductor material,with semiconductor material of the opposite conductivity type interposedtherebetween along the majority carrier trajectories. In manyembodiments parallel current paths are provided through both p-type andn-type drift regions, with immobile electrostatic charge used togenerate a conduction path in one of the parallel current paths.

The disclosed innovations, in various embodiments, provide one or moreof at least the following advantages. However, not all of theseadvantages result from every one of the innovations disclosed, and thislist of advantages does not limit the various claimed inventions.

Reduced on-resistance;

Simpler fabrication;

Improved breakdown voltage; and/or

Better reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIG. 1A and FIG. 1B, in combination, schematically show an example of anactive device which implements some of the inventive teachings of thisapplication.

FIG. 1C schematically shows current flow in the device of FIG. 1A.

FIG. 2 schematically show another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 3 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 4 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 5 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 6 schematically show another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 7 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 8 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 9 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIGS. 10A and 10B, in combination, schematically show another example ofan active device which implements some of the inventive teachings ofthis application.

FIGS. 10C and 10D, in combination, schematically show another example ofan active device which implements some of the inventive teachings ofthis application.

FIG. 11 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 12 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIG. 13 schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIGS. 14A, 14B, 14C, and 14D, in combination, schematically show anotherexample of an active device which implements some of the inventiveteachings of this application.

FIGS. 15A-15L show examples of process steps for building various onesof the disclosed device structures.

FIGS. 16A and 16B, in combination, schematically show another example ofan active device which implements some of the inventive teachings ofthis application.

FIG. 16C schematically shows another example of an active device whichimplements some of the inventive teachings of this application.

FIGS. 17A-17C, in combination, schematically show another example of anactive device which implements some of the inventive teachings of thisapplication.

FIGS. 18A and 18B, in combination, schematically show another example ofan active device which implements some of the inventive teachings ofthis application.

FIG. 19 shows a structure previously proposed by some or all of thepresent inventors.

DETAILED DESCRIPTION OF SAMPLE EMBODIMENTS

The present application discloses several different inventions which invarious ways, whether together or separately, provide improved currentconduction and spread, device reliability and processing simplicity.Many embodiments combine a dynamically inverted channel region with astatically inverted drift region, in separate locations offirst-conductivity-type semiconductor material, with semiconductormaterial of the opposite conductivity type interposed therebetween alongthe majority carrier trajectories.

The numerous innovative teachings of the present application will bedescribed with particular reference to presently preferred embodiments(by way of example, and not of limitation). The present applicationdescribes several inventions, and none of the statements below should betaken as limiting the claims generally.

FIGS. 1A and 1B, in combination, show an example of an n-channel deviceaccording to some of the inventive teachings. The device illustratedincludes trenches 107 which are filled with dielectric material 140containing permanent charge 142. In this particular example, a void 144is located in the interior of the dielectric material 140, but this isnot true of all embodiments.

A gate electrode 150 is located in a shallower trench 109. The gateelectrode is capacitively coupled, through a gate dielectric 151, to ap-type body region 130, so that when a sufficiently positive voltage isapplied to electrode 150, part of body region 130 can be inverted toform a channel. When this occurs, electrons are able to pass from n+semiconductor region 122 through the channel into the n-type epitaxialmaterial 110, and thence (at locations like that shown in FIG. 1A) intothe inverted portion of the p-type region 111.

The p-type region 111 can be formed, for example, by selective epitaxialgrowth or by an angle implant which hits the sidewalls of the trench107, followed by a subsequent drive in step. Further details offabrication will be discussed below.

Since the inversion layer in the p-type region 111 conducts electroncurrent in parallel with the remaining portions of the epitaxial layer110, the p-type regions will be referred to herein as “p-type pillars,”and the n-type epitaxial layer regions which parallel the p-type pillarswill be referred to as “n-type pillars.”

In this example, the p-type pillars 111 are electrically tied to thesource metallization 103 by a connection at some locations (e.g. asshown in FIG. 1B) through a p+ region 136. At other locations, as shownin FIG. 1A, the pillars 111 and the p+ region 136 do not meet; thispermits electrons to flow into the inverted portion of the p-type pillar111.

Note that the region 136 also connects the source metallization to thep-type body region 130.

The permanent charge 142 has a net density near or at thedielectric-to-semiconductor interface which is high enough to invertadjacent portions of the p-type pillar 111. In one example, thepermanent charge 142 has a net charge density of q*1.25E12/cm² where qis the electron charge, and the p-type pillars 111 have a net dopantconcentration of 2.5E16/cm³ and a width of 1 μm.

In the ON state, electrons which flow through the inverted portion ofthe body 130 flow through two paths, in parallel, to the drain diffusion100: some of these electrons flow through the n-type pillars 101, andsome flow through the inverted portions of the p-type pillars 111. Then+ drain is contacted by drain metallization 102. Of course, the entirep-type pillar 111 is not necessarily inverted, so that only a fractionof the pillar 111 carries electron current.

FIG. 1C schematically shows current flow in the device of FIG. 1A.

FIG. 2 shows an alternative embodiment, in which an intermediate layer213 provides lateral conduction between the channel (i.e. the portion ofbody 130 which is inverted by gate 150 in the ON state) and the invertedportion of the p-type pillars 111. In this example, the intermediatelayer 213 has a higher dopant concentration N1 than the copingconcentration N2 of the deeper part of the n-type pillar 101. Thus onecomponent of spreading resistance is reduced, while the voltagewithstand provided by the n-type and p-type drift regions is notdegraded.

FIG. 3 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 1A, except that voids 144 are not used in thisembodiment. Connection of the p-type pillar 111 to the p+ body contactis done, for example, at locations outside of the plane of this drawing,analogously to that shown in FIG. 1B.

FIG. 4 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 1A, except for the presence of a thick bottom oxide452 under the gate electrode 150 in trench 109.

FIG. 5 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 1A, except for the presence of a shield electrode 554under the gate electrode 150 in trench 109. The shield electrode ispreferably connected to the source electrode 103 at some locations ofthe device (not shown). This provides a lower gate-drain capacitanceCgd. Alternatively, the shield electrode can be connected to a differentfixed potential, or otherwise.

FIG. 6 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 3, except for the presence of field plates 646 in thetrenches 107. In this example the field plates 646 are tied to thesource metal 103, but other biasing can be used if desired. In thisexample the field plates 646 are made of heavily doped polysilicon.

FIG. 7 shows a MOS transistor which is generally somewhat similar to thestructure shown in FIG. 1B, except for the presence of a recessed sourcecontact: a recess 705 has been etched over the top of trench 107, beforethe source metallization 103 is formed. The location shown has aconnection from the p-type pillar 111 to the p+ body contact 136 (likethat in FIG. 1B), but at other locations the tops of pillars 111 wouldnot merge with the p+ 136.

FIG. 8 shows another active device structure which is generally somewhatsimilar to that shown in FIG. 1A, except that a much deeper trench 809replaces the gate trench 109, and a deep T-shaped gate electrode 850replaces the gate electrode 150. Note that the deeper part of theT-shaped gate electrode is surrounded by a dielectric 853 which isthicker than the gate dielectric 151. This family of structures providesa higher doping in N region 101, and hence lower specific on-resistanceR_(SP), without degrading breakdown voltage.

FIG. 9 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 8, except that for the presence, in the deep gatetrenches 809, of a shield electrode 954. This is preferably made ofpolysilicon material tied to the source electrode.

FIGS. 10A and 10B, in combination, show a MOS transistor whichimplements the intermediate conduction layer and paralleled driftpillars with a planar gate electrode 1050.

FIGS. 10C and 10D, in combination, show a MOS transistor which issomewhat similar to that shown in FIGS. 10A and 10(B), except that the Ppillars have stepped or variable doping concentrations.

FIG. 11 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 10B, except for the presence of a shield electrode1154 which is connected to the source electrode.

FIG. 12 shows a MOS transistor which is generally somewhat similar tothat shown in FIG. 10B, but with a different planar gate configuration.Note that majority carrier injection is located closer to the p-pillar(rather than over the N-pillar), as compared to the embodiment of FIG.10A.

FIG. 13 shows a MOS transistor with trenches filled with dielectricmaterial containing permanent charge and the gate electrode in aseparate shallower trench. This is an example of an inventive embodimentwhich includes the npnpn structure of FIG. 1A, including the staticinversion of a p-type drift region by immobile net electrostatic charge,but which does NOT include parallel conduction through both n-type andp-type drift regions.

Lateral Devices

FIGS. 14A, 14B, 14C, and 14D, in combination, schematically show anexample of a lateral device which implements some of the inventiveteachings of this application.

FIG. 14A shows a top view of a new lateral power MOSFET structure withtrenches filled with dielectric layer that contain permanent charges.

FIG. 14C shows a section of this device, along line C-C. In thisstructure, a stepped gate 1450 controls inversion of a p-type bodyregion 1430, to selectively allow conduction. In the ON state, electronspass from source region 1422 through the inverted portion of body region1430 (i.e. through the channel), and thence through intermediate region1413, through n-type drift region 1402, and thence to drain 1400. Notethat there is not a junction between the n-type regions 1402 and 1413;preferably 1413 has a higher net doping than 1402, but this is optional.A substrate metallization 1496 provides backside contact to a substrate1490.

Many, but not all, of the features visible in FIG. 14C are electricallyanalogous to components of the various vertical device embodimentsdescribed above. However, there is more to the device than this.

FIG. 14D shows a section along line BB of this device. Dielectric 1440blocks conduction in the plane shown. However, dielectric 1440preferably contains an immobile net electrostatic charge, either in itsbulk or at its interfaces (above and below the plane of this drawing).

FIG. 14B shows a section along line AA. Here the p-type drift regionportion 1411 is visible. Parts of region 1411 which border thedielectric 1440 will be inverted by the immobile net electrostaticcharge in dielectric 1440. The surface dielectric layer 1441 as shown inFIG. 14B can optionally contain an immobile net electrostatic chargewhich creates a surface electron inversion layer at the interface withthe P drift layer 1411. This provides an additional current path fromchannel to drain and results in a lower R_(SP).

Returning now to the top view of FIG. 14A, it can be seen that the twodrift region portions 1411 and 1401 provide paralleled drift regions ofopposite types. This helps to improve on-state conductivity. The chargebalance resulting from the use of these complementary types also helpsimprove breakdown.

Process Example

FIGS. 15A-15L show examples of process steps for building various onesof the disclosed device structures.

The starting material can be, for example, an n-on-n+ epitaxialstructure, as shown in FIG. 15A.

An n-type implant can now be performed, as shown in FIG. 15B, and thendriven in by heat treatment, to form the intermediate layer 213.

The shallow trenches 109 are then etched, and the gate oxide 151 isgrown. This results in the structure of FIG. 15C.

The material for the gate electrode 150, e.g. polysilicon, is thendeposited and etched back. This results in the structure of FIG. 15D.

The p-type body regions 130 and the n+ source regions 122 are thenimplanted. This results in the structure of FIG. 15E.

An optional deep P+ region 236 is then implanted and annealed. Thisresults in the structure of FIG. 15F.

Deep trenches 107 are then etched. This results in the structure of FIG.15G.

The p-type pillars 111 are then formed by lateral growth ofin-situ-doped p-type material. (Alternatively, implantation andactivation can be used instead.) This results in the structure of FIG.15H.

An oxide growth step is now performed, to form part of the oxide 144 onthe sidewalls of the deep trenches 107. (Note that this growth step ispreferably not prolonged enough to fill the trench.) An angle implant isnow performed, e.g. of Cs+, to introduce the charged ions which willprovide the net electrostatic charge 142. Note that these ions arepreferably not dopant ions for the semiconductor material, and most ofthis implant will not even reach the semiconductor material. Thisresults in the structure of FIG. 15I.

Trench filling can now be completed. This can be done with an oxidegrowth or deposition step to leave a void in place, or with apolysilicon deposition to form a field plate (as in FIG. 6), or with aslow oxidation to totally fill the trench. This results in the structureof FIG. 15J.

A pad layer of polysilicon is now deposited, and an anneal is performedto activate dopants and densify oxide. This results in the structure ofFIG. 15K.

In this example, a recess is now etched for the recessed contact, andsource metallization 103 is now deposited. This results in the structureof FIG. 15L.

Examples of IGBT Structures

The disclosed inventions are applicable to a wide variety of devicestructures. One of these is IGBTs, which have bipolar conduction (i.e.using both electrons and holes).

FIG. 16A shows an IGBT transistor, in which a P+ diffusion 1694, and ann-type buffer layer 1692, have replaced the N+ drain 100 in the deviceof FIG. 1A. When the device is off, the combination of p-type pillar 111with n-type pillar 101 and electrostatic charge 142 improves thebreakdown voltage here, just as it does in the device of FIG. 1A.

In the ON state, the P+ diffusion 1694 will act as an emitter for holes.That is, the n-type buffer layer 1692 and the N pillar region 101 willact as the base of a PNP bipolar transistor: electron current whicharrives at the junction between regions 1692 and 1694 will cause someemission of holes, which provide another component of current.(Upwardly-flowing holes carry electrical current in the same directionas downwardly-flowing electrons, so the hole current adds to the totalconduction of the device.) The hole current results in the conductivitymodulation of the N pillar 101 which lowers its resistivity. The holecurrent can also pass through the p-type pillars 111 and the p+ regions136 to reach the emitter metallization 1604. This can provide higherlatchup current and faster turn-off speed of the device.

FIG. 16B shows how the p-type pillars extend up to connect with the p+diffusions at some locations.

FIG. 16C shows an IGBT transistor which is generally similar to that ofFIG. 16A, but also includes an intermediate layer 213 where the n-typedoping is heavier than in the drift region portion 101. This reduces theon-state series resistance seen by the electron current, while notdegrading the on-state series resistance seen by the hole current (whichdoes not pass through region 213).

In the example shown, a void 144 is included in the trench dielectric140, to reduce parasitic capacitance. However, the trench dielectric 140can be made solid instead, or can be made from multiple dielectriclayers.

This IGBT structure, as compared to a more conventional IGBT, wouldprovide better specific on-resistance, higher latchup current, andfaster turn-off.

FIGS. 17A-17C, in combination, show a lateral IGBT which incorporatessome of the inventive teachings of this application. In many ways thegeometry of this device is similar to that of the lateral device ofFIGS. 14A-14D, except for the presence of the P+ diffusion 1794 whichcontacts the collector metallization 1606, and acts as an emitter forholes. An N+ buffer region 1792 and n-type transition region 1793 alsohelp connect the collector metallization 1606 to the current through thedrift region.

P+ diffusion 1794 preferably has an electrical connection to the stripes1411 at some locations, but this is not present at the location shown.

FIG. 17A shows a top view of this device.

FIG. 17B shows a cross section along line AA of the device shown in FIG.17A.

FIG. 17C shows a cross section along CC of the device shown in FIG. 17A

Single-Trench Embodiment

FIGS. 18A and 18B, in combination, show another active device. In theseFigures, only one type of trench is used in the active device area,rather than the trenches 107 and 109 used in FIG. 1A.

In this device the gate is located in a deep trench 1809. The trench1809 includes fixed charge in its dielectric, to invert the portions ofp-type pillars 111 which are next to the trench 1809. Since the p-typepillars do merge with the body regions 130 in some locations (as shownin FIG. 18B), and not in other locations (as shown in FIG. 18A), theadvantages of paralleled drift region portions are obtained in thisstructure too.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: afirst-conductivity-type semiconductor source region; asecond-conductivity-type semiconductor body region; a gate electrode,which is capacitively coupled to invert a portion of said body region; asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor portions in parallel;immobile electrostatic charge which is capacitively coupled to invertparts of said second-conductivity-type drift region portions; and afirst-conductivity-type semiconductor drain region; wherein said bodyregion is interposed between said source region and said drift region;and wherein said drift region is interposed between said body region andsaid drain region; and further comprising an intermediate layer whichhas a first conductivity type, and has a higher doping than saidfirst-conductivity-type semiconductor portion, and which connects saidchannel to both said first-conductivity-type and saidsecond-conductivity-type semiconductor portions; whereby, in the ONstate, majority carriers flow both through said first-conductivity-typeportions and said second-conductivity-type portions of said drift regionin parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: ann-type semiconductor source region; a p-type semiconductor body region;a gate electrode, which is capacitively coupled to invert a portion ofsaid body region; a semiconductor drift region which includes bothn-type and p-type semiconductor portions electrically connected inparallel; immobile positive ions which are capacitively coupled tojointly invert parts of said p-type drift region portions; and an n-typesemiconductor drain region; wherein said body region is interposedbetween said source region and said drift region; and wherein said driftregion is interposed between said body region and said drain region; andfurther comprising an n-type intermediate layer which has a higherdoping than said n-type semiconductor portion of said drift region, andwhich connects said channel to both said first-conductivity-type andsaid second-conductivity-type semiconductor portions; whereby, in the ONstate, electrons flow both through said n-type portions and said p-typeportions of said drift region in parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: afirst-conductivity-type semiconductor source region; asecond-conductivity-type semiconductor body region; a gate electrode,which is capacitively coupled to invert a portion of said body region; asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor portions in parallel;immobile electrostatic charge which is capacitively coupled to invertparts of said second-conductivity-type drift region portions; and afirst-conductivity-type semiconductor drain region; wherein said bodyregion is interposed between said source region and said drift region;and wherein said drift region is interposed between said body region andsaid drain region; whereby, in the ON state, majority carriers flow boththrough said first-conductivity-type portions and saidsecond-conductivity-type portions of said drift region in parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: ann-type semiconductor source region; a p-type semiconductor body region;a gate electrode, which is capacitively coupled to invert a portion ofsaid body region; a semiconductor drift region which includes bothn-type and p-type semiconductor portions electrically connected inparallel; immobile positive point charges which are capacitively coupledto jointly invert parts of said p-type drift region portions; and ann-type semiconductor drain region; wherein said body region isinterposed between said source region and said drift region; and whereinsaid drift region is interposed between said body region and said drainregion; whereby, in the ON state, electrons flow both through saidn-type portions and said p-type portions of said drift region inparallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: afirst-conductivity-type semiconductor source region; asecond-conductivity-type semiconductor body region; a generally planargate electrode, which is capacitively coupled to invert a portion ofsaid body region to define a predominantly horizontal channel therein; asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor pillars in parallel; immobileelectrostatic charge which is capacitively coupled to invert parts ofsaid second-conductivity-type drift region portions; and afirst-conductivity-type semiconductor drain region; wherein said bodyregion is interposed between said source region and said drift region;and wherein said drift region is interposed between said body region andsaid drain region; and wherein, in the ON state, majority carriers flowboth through said first-conductivity-type and saidsecond-conductivity-type pillars in parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: ann-type semiconductor source region; a p-type semiconductor body region;a planar gate electrode, which is capacitively coupled to invert aportion of said body region to define a predominantly horizontal channeltherein; a semiconductor drift region which includes both n-type andp-type semiconductor pillars in parallel; immobile electrostatic chargewhich is capacitively coupled to invert parts of said p-type driftregion portions; and an n-type semiconductor drain region; wherein saidbody region is interposed between said source region and said driftregion; and wherein said drift region is interposed between said bodyregion and said drain region; and wherein, in the ON state, majoritycarriers flow both through said n-type and said p-type pillars inparallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: afirst-conductivity-type semiconductor source region; asecond-conductivity-type semiconductor body region; a gate electrode,which is capacitively coupled to invert a horizontal portion of saidbody region; a semiconductor drift region which includes bothfirst-conductivity-type and second-conductivity-type semiconductorstripes in parallel; a trench, containing immobile electrostatic chargewhich is capacitively coupled to invert parts of saidsecond-conductivity-type stripes; and a first-conductivity-typesemiconductor drain region; wherein said body region is interposedbetween said source region and said drift region; and wherein saidfirst-conductivity-type and second-conductivity-type semiconductorstripes are each laterally interposed between said body region and saiddrain region; whereby, in the ON state, majority carriers flow boththrough said first-conductivity-type and said second-conductivity-typestripes in parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A semiconductor device, comprising: afirst-conductivity-type semiconductor source region; asecond-conductivity-type semiconductor body region; a gate electrode,which is capacitively coupled to invert a portion of said body region; asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor portions in parallel;immobile electrostatic charge which is capacitively coupled to invertparts of said second-conductivity-type drift region portions; afirst-conductivity-type semiconductor buffer region; and asecond-conductivity-type semiconductor minority-carrier-emitter region;wherein said body region is interposed between said source region andsaid drift region; and wherein said drift region is interposed betweensaid body region and said drain region; whereby, in the ON state,majority carriers flow both through said first-conductivity-typeportions and said second-conductivity-type portions of said drift regionin parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A method of operating a powersemiconductor device, comprising: passing majority carriers from afirst-conductivity-type semiconductor source, through a portion of asecond-conductivity-type semiconductor body region which has beeninverted by the applied voltage on a gate electrode, into afirst-conductivity-type semiconductor intermediate region; passing someones of said majority carriers, from said intermediate region, throughsaid first-conductivity-type portions, and passing others of saidmajority carriers through parts of said second-conductivity-typesemiconductor portions which have been inverted by immobileelectrostatic charge, to a first-conductivity-type semiconductor drainregion; and further comprising an intermediate layer which has a firstconductivity type, and has a higher doping than saidfirst-conductivity-type semiconductor portion, and which connects saidchannel to both said first-conductivity-type and saidsecond-conductivity-type semiconductor portions; whereby, in the ONstate, majority carriers flow both through said first-conductivity-typeportions and said second-conductivity-type portions of said drift regionin parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A method of operating a powersemiconductor device, comprising: passing majority carriers from afirst-conductivity-type semiconductor source, through a portion of asecond-conductivity-type semiconductor body region which has beeninverted by the applied voltage on a gate electrode, into afirst-conductivity-type semiconductor intermediate region; passing someones of said majority carriers, from said intermediate region, throughsaid first-conductivity-type portions, and passing others of saidmajority carriers through parts of said second-conductivity-typesemiconductor portions which have been inverted by immobileelectrostatic charge, to a first-conductivity-type semiconductor drainregion; and further comprising an intermediate layer which has a firstconductivity type, and has a higher doping than saidfirst-conductivity-type semiconductor portion, and which connects saidchannel to both said first-conductivity-type and saidsecond-conductivity-type semiconductor portions; whereby, in the ONstate, majority carriers flow both through said first-conductivity-typeportions and said second-conductivity-type portions of said drift regionin parallel.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A method of operating a powersemiconductor device, comprising, in the ON state: passing majoritycarriers from a first-conductivity-type semiconductor source, through aportion of a second-conductivity-type semiconductor body region whichhas been inverted by the applied voltage on a gate electrode, into asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor portions in parallel; andpassing some ones of said majority carriers through saidfirst-conductivity-type portions, and passing others of said majoritycarriers through parts of said second-conductivity-type semiconductorportions which have been inverted by immobile electrostatic charge, to afirst-conductivity-type semiconductor drain region.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: A method of operating a powersemiconductor device, comprising, in the ON state: passing majoritycarriers from a first-conductivity-type semiconductor source, through aportion of a second-conductivity-type semiconductor body region whichhas been inverted by the applied voltage on a gate electrode, into asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor portions in parallel; andpassing some ones of said majority carriers through saidfirst-conductivity-type portions, and passing others of said majoritycarriers through parts of said second-conductivity-type semiconductorportions which have been inverted by immobile electrostatic charge,through a first-conductivity-type semiconductor buffer region, to asecond-conductivity-type minority-carrier-emitter region; and passingminority carriers from said minority-carrier-emitter region throughparts of said second-conductivity-type semiconductor portions which havenot been inverted, and through additional second-conductivity-typeregions, to a contact which is also electrically connected to saidsource region.

According to some (but not necessarily all) of the disclosed innovativeembodiments, there is provided: Power semiconductor devices, and relatedmethods, where majority carrier flow is divided into paralleled flowsthrough two drift regions of opposite conductivity types.

MODIFICATIONS AND VARIATIONS

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a tremendous range of applications, and accordingly the scope ofpatented subject matter is not limited by any of the specific exemplaryteachings given. It is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

For one example, the examples described above are generally n-channeldevices, in which electrons are the majority carriers; but the disclosedinnovations can also be applied to p-channel devices, in which holes arethe majority carriers.

For another example, the examples described above are implemented insilicon; but in alternative embodiments, the disclosed innovations canalso be implemented in other semiconductors such Ge, SiGe, GaAs or otherIII-V compound semiconductors (including ternary and quaternary alloys),SiC or other Group IV semiconducting alloys, etc. etc.

In other contemplated embodiments, various doped regions can have gradeddopant concentrations.

In various other embodiments, a wide variety of other semiconductorregions and connections can be added if desired.

In various other embodiments, a wide variety of other semiconductorregions and connections can be added if desired.

The two IGBT embodiments described in detail above are merely examplesof the many possible structures which include at least some degree ofbipolar conduction.

Additional general background, which helps to show variations andimplementations, as well as some features which can be synergisticallywith the inventions claimed below, may be found in the following U.S.patent applications. All of these applications have at least some commonownership, copendency, and inventorship with the present application:All of these applications, and all of their priority applications, arehereby incorporated by reference: US20080073707; US20080191307;US20080164516; US20080164518; US20080164520; US20080166845;US20090206924; US20090206913; US20090294892; US20090309156;US20100013552; US20100025726; US20100025763; US20100084704;US20100219462; US20100219468; US20100214016; US20100308400;US20100327344; US20110006361; US20110039384; US20110079843; and U.S.application Ser. Nos. 12/369,385; 12/431,852; 12/720,856; 12/806,203;12/834,573; 12/835,636; 12/887,303; 12/939,154; 13/004,054; and13,089,326. Applicants reserve the right to claim priority from theseapplications, directly or indirectly, and therethrough to even earlierapplications, in all countries where such priority can be claimed.

None of the description in the present application should be read asimplying that any particular element, step, or function is an essentialelement which must be included in the claim scope: THE SCOPE OF PATENTEDSUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none ofthese claims are intended to invoke paragraph six of 35 USC section 112unless the exact words “means for” are followed by a participle.

The claims as filed are intended to be as comprehensive as possible, andNO subject matter is intentionally relinquished, dedicated, orabandoned.

What is claimed is:
 1. A method of operating a power semiconductordevice, comprising: passing majority carriers from afirst-conductivity-type semiconductor source, through a portion of asecond-conductivity-type semiconductor body region which has beeninverted by the applied voltage on a gate electrode, into afirst-conductivity-type intermediate region; passing some ones of saidmajority carriers, from said first-conductivity-type intermediateregion, through first-conductivity-type drift region portions, andpassing others of said majority carriers through parts ofsecond-conductivity-type drift region portions which have been invertedby immobile electrostatic charge, to a first-conductivity-typesemiconductor drain region; wherein said first-conductivity-typeintermediate region has a higher doping than saidfirst-conductivity-type drift region portions, and connects said channelto both said first-conductivity-type and said second-conductivity-typedrift region portions; whereby, in the ON state, majority carriers flowboth through said first-conductivity-type and saidsecond-conductivity-type drift region portions in parallel.
 2. Themethod of claim 1, wherein said first-conductivity-type source region isn-type, and said majority carriers are electrons.
 3. The method of claim1, wherein said source, body, intermediate, and drain regions aresilicon.
 4. The method of claim 1, wherein said immobile electrostaticcharge is provided by cesium ions.
 5. The method of claim 1, whereinsaid immobile electrostatic charge consists of point charges.
 6. Themethod of claim 1, wherein said immobile electrostatic charge isprovided by ions in dielectric material and/or by ions at adielectric/semiconductor interface.
 7. The method of claim 1, whereinsaid immobile electrostatic charge is provided by ions in dielectricmaterial in a trench.
 8. The method of claim 1, wherein saidsecond-conductivity-type drift region portions have inhomogeneousdoping, such that less heavily doped portions thereof are inverted bysaid immobile electrostatic charge.
 9. A method of operating a powersemiconductor device, comprising, in the ON state: passing majoritycarriers from a first-conductivity-type semiconductor source, through aportion of a second-conductivity-type semiconductor body region whichhas been inverted by the applied voltage on a gate electrode, into asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type drift region portions in parallel; andpassing some ones of said majority carriers through saidfirst-conductivity-type drift region portions, and passing others ofsaid majority carriers through parts of said second-conductivity-typedrift region portions which have been inverted by immobile electrostaticcharge, to a first-conductivity-type semiconductor drain region.
 10. Themethod of claim 9, wherein said first-conductivity-type source region isn-type, and said majority carriers are electrons.
 11. The method ofclaim 9, wherein said source, body, intermediate, and drain regions aresilicon.
 12. The method of claim 9, wherein said immobile electrostaticcharge is provided by cesium ions.
 13. The method of claim 9, whereinsaid immobile electrostatic charge consists of point charges.
 14. Themethod of claim 9, wherein said immobile electrostatic charge isprovided by ions in dielectric material and/or by ions at adielectric/semiconductor interface.
 15. The method of claim 9, whereinsaid immobile electrostatic charge is provided by ions in dielectricmaterial in a trench.
 16. The method of claim 9, wherein saidsecond-conductivity-type drift region portions have inhomogeneousdoping, such that less heavily doped portions thereof are inverted bysaid immobile electrostatic charge.
 17. A method of operating a powersemiconductor device, comprising, in the ON state: passing majoritycarriers from a first-conductivity-type semiconductor source, through aportion of a second-conductivity-type semiconductor body region whichhas been inverted by the applied voltage on a gate electrode, into asemiconductor drift region which includes both first-conductivity-typeand second-conductivity-type semiconductor drift region portions inparallel; and passing some ones of said majority carriers through saidfirst-conductivity-type drift region portions, and passing others ofsaid majority carriers through parts of said second-conductivity-typedrift region portions which have been inverted by immobile electrostaticcharge, through a first-conductivity-type semiconductor buffer region,to a second-conductivity-type minority-carrier-emitter region; andpassing minority carriers from said minority-carrier-emitter regionthrough parts of said second-conductivity-type drift region portionswhich have not been inverted, and through additionalsecond-conductivity-type regions, to a contact which is alsoelectrically connected to said source region.
 18. The method of claim17, wherein said first-conductivity-type source region is n-type, andsaid majority carriers are electrons.
 19. The method of claim 17,wherein said source, body, intermediate, and drain regions are silicon.20. The method of claim 17, wherein said immobile electrostatic chargeis provided by cesium ions.